Abstract
We report the numerical investigation of strain induced superconductor-insulator quantum phase transition on a Lieb lattice. Based on a non perturbative Monte Carlo technique, we show that in two dimensions an s-wave superconductor undergoes transition to a highly correlated bosonic insulator under the influence of strain, applied as staggered hopping amplitudes. We further demonstrate a strain induced BCS-BEC like crossover in the superconducting state, such that the superconductor-insulator transition takes place between a bosonic superconductor and a bosonic insulator. Our results suggest that it is the contribution of the dispersive bands towards the superconducting order, which dictates this crossover. To the best of our knowledge, this is the first work to report theoretical investigation of "disorder free" superconductor-insulator phase transition in systems with Lieb lattice structure. With the recent experimental realization of the Lieb lattice in ultracold atomic gases, photonic lattices as well as in solid state systems, we believe that the results presented in this paper would be of importance to initiate experimental investigation of such novel quantum phase transitions. We further discuss the fate of such systems at finite temperature, highlighting the effect of fluctuations on the superconducting pair formations, thermal scales and quasiparticle behavior. Our non perturbative numerical approach to the problem enables us to capture the thermal scales of the system accurately and provides us with mean field estimates of the ground state properties. The high temperature quasiparticle signatures discussed in this paper are expected to serve as benchmarks for experiments such as radio frequency and momentum resolved radio frequency spectroscopy measurements carried out on systems such as ultracold atomic gases.
Highlights
Tuning the quantum behavior of a material by applying force via external strain has been in the forefront of research in condensed matter systems, over the past few years [1,2,3,4,5,6,7]
The high-temperature pseudogap regime is restricted at η → 0, suggesting that strain renders the spectral gap at the Fermi level immune to thermal fluctuations
We discuss the BCS-BEC crossover on the Lieb lattice in the following few sections and focus on a specific interaction strength of this crossover regime to demonstrate the effect of strain, in the later sections of the paper
Summary
Tuning the quantum behavior of a material by applying force via external strain has been in the forefront of research in condensed matter systems, over the past few years [1,2,3,4,5,6,7]. Interaction significantly renormalizes the behavior of the superconducting order even at the ground state and a single unit cell approach to the problem is insufficient to capture such renormalizations This leaves a gap in our understanding of the physics of superconductors on a flat band Lieb lattice, even for an unstrained or isotropic system, and demands for a theoretical investigation to address these issues. This is followed by the conclusions drawn based on this work
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